There’s an ‘Expand all comments’ link. Personally I find the community there to be a nice complement to HN. Less serious, less important issues, more usable when tired.

Quality. It's often "sketchy at best".

As for design, there's "Expand All" up the top right of the comments. But yes, the "hidden by default" arrangement is a bit nuts.

I find it just as surprising that HN doesn't allow you to collapse a comment chain. I use a GreaseMonkey script to do it on my desktop, but when browsing from a mobile device I have to scroll down until I can find the next root comment.